Red Moon During Lunar Eclipse

This is a photograph (credits to Hemant Hariyani) taken during a lunar eclipse. Besides being a very beautiful sight, there’s a curious orange tinge on the lower left quadrant of the moon. My curiosity lead to the moonzoo (please search for the terms “blood red” on that page to see their reason) – which explains very briefly the cause of this. While discussing on a list, I realized that it’s confusing sometimes to visualize how exactly this happens – so I drew a diagram to get this straightened out.

Refraction causes light to bend – and when different colors of white light bend at different angles, that causes light to split up; the very cause of rainbows. This is enough theory, the rest is self explanatory in the diagram beside this text. As you can figure out, light from the sun, reflected refracted when passing through earth’s atmosphere – falls on the moon (and since only longer λ [red] reach out) it looks orange (or blood red).

It’s imperative to note, that the cause of this blood red color is very different from the cause of the blood red color we see when the moon rises on certain nights. That blood red is caused because the light coming from the moon gets scattered when passing through the earth’s atmosphere (more so, polluted atmosphere), which causes the red waves to fall on our eyes and make the moon look red. That is when the light from the sun gets reflected back on earth and on it’s way to our eyes, we see red (the whole thing looks red – unlike this phenomenon).